(Not Applicable)
The present invention relates generally to the art of acoustics, and more particularly to a diffusion apparatus which is adapted to facilitate a reduction of pressure in a fluid flow while simultaneously suppressing or silencing jet velocity noise by eliminating the noise-generating sources created by the flow.
For many years, vent silencers and diffusers have been employed in various industries to muffle high velocity air or gas, including steam, flowing to the atmosphere. For example, vent silencers are often used in conjunction with the safety valves employed in high pressure, high temperature steam service for relieving over pressure from steam generating equipment. In this regard, it is not uncommon for the discharge from such high capacity safety valves to achieve sonic or near sonic velocity in the discharge duct leading to atmosphere such that the duct flow transmits the noise created at the valve, as well as the noise generated as a result of the discharge of the flow to atmosphere. Various federal regulations have been created which stringently regulate the noise level which may be generated by such discharging safety valves. As a result, there has been developed in the prior art various types of vent or blowoff silencers and diffusers which are adapted to muffle a sonic gas, steam, or air stream. In the prior art, vent silencers are often used in an approach known as the xe2x80x9cpath treatmentxe2x80x9d of noise. In the path treatment approach, noise-generation is allowed to take place, with the noise-absorbing elements of the vent silencer being operative only to absorb the noise that has already physically been generated. Many currently known vent silencers achieve noise reduction through the use of elements such as wire-mesh, metal foam, or mineral wool acoustic cladding.
An alternative approach to noise reduction is known as xe2x80x9csource treatmentxe2x80x9d. The source treatment approach relies on reducing the strength of the source of noise by various means, including the control or reduction of fluid velocity. Currently known diffusers are often used in source treatment applications, and include wire meshes, metal foam, or equivalents which are placed into the flow path of the gas, steam or air jet in such a way that the noise-generating mechanisms are weakened to a point that a high degree of noise reduction is achieved.
In current vent silencer and diffuser designs, features are included to facilitate a reduction in the flow velocity at the entrance to the wire mesh or other noise reducing elements. More particularly, the flow is typically channeled through a first pressure-reducing stage to facilitate a pressure-drop to critical or near-critical values. In some vent silencer and diffuser designs, when the pressure drop requirement is very high, an additional pressure drop stage is introduced at the inlet without the treatment of the resulting supersonic jet(s) and without any wire meshes or other noise reducing/sound absorbing elements before introduction into the next stage(s). In this respect, only the downstream stage(s) that follow have elements to muffle the noise that has been generated.
Though generally suitable for achieving noise reduction either through noise absorption in a path treatment application or velocity control/pressure reduction in a source treatment application, prior art vent silencers and diffusers possess certain deficiencies which detract from their overall utility. Perhaps the most significant of these deficiencies is the current practice of placing the wire mesh or other noise reduction elements directly at (i.e., in direct contact with) the outlets and/or inlets of the flow openings or passages within the pressure reducing stages. Such placement often results in blockage at the outlets of the flow openings when solids are present in the flow stream larger than the openings in the wire mesh or its functional equivalent. The placement of the noise reduction element directly at the inlet end of a flow opening of another pressure reducing stage results in an efficiency decrease in the losses which would otherwise be achieved if flow to the inlet end was unrestricted.
The present invention addresses these deficiencies by providing a diffuser apparatus which falls within the source treatment category and is adapted to facilitate noise reduction through a reduction of peak velocity at the outlet of a pressure reduction flow path.
The diffuser apparatus of the present invention is adapted for use in conjunction with highly underexpanded jets. If allowed to expand freely when exiting from a flow opening or passage, these underexpanded jets facilitate supersonic flow with resultant noise producing shockwaves downstream of the sleeve passage exit or outlet. The diffuser of the present invention facilitates noise reduction via a reduction of peak velocity at the outlet of a pressure reduction sleeve passage through the use of wire mesh, metal foam or other noise-absorbing elements in conjunction with a straight or tortuous pressure reducing sleeve passage. The use of the wire meshes, metal foam or their functional equivalents in accordance with the present invention makes the flow more uniform at the outlet of the sleeve passage, thereby reducing the magnitude of the velocity peak. Since noise is strongly related to velocity, the reduction in the peak velocity in turn achieves a reduction in noise.
In the diffuser apparatus of the present invention, the wire mesh or its functional equivalents used to eliminate the noise sources in the flow is oriented within the apparatus so that the outlets and/or inlets of the sleeve passage(s) within the pressure reducing stage(s) are unrestricted. The lack of any restriction at the outlet(s) of the sleeve passage allows for the passage of any solids in the fluid stream out of the jet exit with the flow. This feature has no significant impact on the function of noise reduction due to the manner in which a shock wave is produced by the jet emanating from the outlet of the sleeve passage. The lack of any restriction at the inlet end of the sleeve passage(s) of a downstream pressure reducing stage effectively maintains the level of inlet losses achieved as a result of flow into such sleeve passage(s).